1. Field of Invention
A method and apparatus for improving the flexible connection between low pressure turbines and condensers, and the like, involving a modified belt type expansion joint and an in situ fluid sealant.
2. Brief Description of the Prior Art
The belt type expansion joint commonly is used as the flexible connection between low pressure turbines and steam condensers in power plants, both fossil and nuclear. The belt itself is shaped like a dog bone, with a longitudinal central section and a bead edge at either end. Such an expansion joint typically can accommodate up to one inch of longitudinal compression travel between wall sections, and a half inch of lateral deflection. However, it is well-known that a dog bone belt cannot accommodate any longitudinal extension travel, after being mounted. Hence, it has been a critical design criteria to tightly control the longitudinal spacing between two clamping bar assemblies so as to remain within the belt manufacturer's specifications for a given belt type expansion joint.
Such belts have long been designed and manufactured by La Favorite Industries, Hawthorne, N.J. The belt typically comprises a composite of tire cording and vulcanized rubber with a first edge bead and a second edge bead. The belts typically are sized in increments between 6-10 inches in overall height, have a central portion between 3/8 and 5/8 inches thick, and include cylindrical bead edges that typically are standardized at about 1.250" inches in diameter, both at the top and at the bottom.
The removable clamping bar, as well as the clamping surface fixed to a condenser or turbine wall structure, also typically cooperate to define a cylindrical cavity with an inner diameter of about 1.125 inches. That cavity between the clamping bar and the wall clamping surface is intended to tightly engage the edge bead, when the clamp is fastened. However, as noted before, there is a critical longitudinal dimension between the first cavity and the second cavity, and this dimension cannot initially be smaller than the corresponding dimension between the two edge beads of an inserted dog bone. Accordingly, there always is a zero plus tolerance for the expansion joint height, with respect to the height of the dog bone, and up to a 1/2 inch minus tolerance.
The clamping surface which becomes part of a condenser or turbine wall structure must be field welded in place, and often times that clamping recess will be at an improper angle or otherwise will shift after installation. Furthermore, years of thermal cycling in the power plant, or settling of plant and equipment, can shift or move either the turbine or the condenser. Hence, that critical dimension can easily be altered from a design point. Since the dog bone belt cannot accommodate any extension beyond its design height, power plants typically have to perform expensive modifications, where an unacceptable misalignment situation arises.
Accordingly, to replace such an expansion joint, the entire circumference served by the expansion joint must carefully be field-measured and a replacement dog bone selected that will be within the design tolerances. A dog bone typically is designed to accept a maximum one inch in cyclical axial compression, due to thermal expansion and contraction effects. However, it should be appreciated that if there is an initial misalignment during installation of the clamping bars, the desired one inch compression range seriously will be impaired. If the dog bone has an installed bow (because the clamping bars are too close together) that initial bow will tend to cause premature failure of the rubber and cording, due to excessive flexure. If the dog bone is installed too tightly, as by a transverse misalignment greater than the design misalignment permitted, the shoulder of each clamp will make a line contact with the bead, leaving inadequate sealing contact between the bead edge and its surrounding cavity. With less than a full circular surface seal, significant leakage of air into the condenser structure will occur, and the mixing of air with steam seriously degrades condenser performance.
MERZ (U.S. Pat. No. 4,063,755) illustrates another compensator or expansion joint wherein a planar belt is bolted outside of a sealing cavity filled with flexible fabrics and thermally sensitive materials, so as to protect the outwardly mounted rubber belt. In this solution a different mounting is required, and an existing dog bone cannot be replaced with such a seal.
It also generally is known that a fluid elastomeric material may have value as a sealant, in a space between parts subject to relative movement forces. LIFFERTH (U.S. Pat. No. 4,050,700) illustrates injection of a fluid sealant under pressure through a Zirk type fitting, into a void between two metal parts. BRIEGER (U.S. Pat. No. 4,203,607) illustrates an elastomeric packing comprising a large size grit to minimize extrusion of an O-ring into a clearance space. Likewise, HINDS (U.S. Pat. No. 3,445,393) discusses how various large, flake-like copolymer materials have utility as a packing material, where there is a potential of escape through a clearance space.